code: def is_missing(value):
      """
      Used to check whether a dataclass field has ever been assigned.
  
      If a field without default value has never been assigned, it will have a special value ``MISSING``.
      This function checks if the parameter is ``MISSING``.
      """
      # MISSING is not singleton and there is no official API to check it
      return isinstance(value, type(dataclasses.MISSING))
  
file_path: nni/nni/experiment/config/utils/public.py
imports: import dataclasses
  import math
  from pathlib import Path
  from typing import Union
label_desc: Use image node_id 1 for calling a global function with example usage: is_missing(value) and returns: isinstance